1. Field of the Invention
The subject matter of the invention relates to the construction and method of fabricating laminated structures of the type wherein a plurality of materials are joined together to provide an integral structure having the composite physical and chemical characteristics of the materials utilized. The invention is more specifically concerned with composites predominantly utilizing synthetic or nonmetallic materials, such as high strength fibers, open-cell resinous foams, and thermosetting resins.
As new combinations of materials are sought in composite laminar structures, frequent difficulty is experienced both in initially bonding the materials together and also in maintaining laminar integrity in subsequent use. Particularly where mechanical rather than chemical bonding is relied upon in fabricating laminated structures, delamination in use is a common problem. As more or different laminar or sheet materials are employed, interface bond strength is affected not only by the chemical compatibility between the laminates and the bonding material but also by certain physical characteristics such as dissimilar coefficients of expansion. It is also important to composite integrity that discrete laminar interfaces be eliminated and that composite penetration by deleterious liquids be prevented. It is found that the fewer chemically and physically dissimilar materials used and the fewer molding steps required in forming laminar composites, the greater likelihood of maintaining the ultimate integrity of the resultant structure.
One of the most broadly promising applications for the use of composite structures comprised mainly of plastic or synthetic materials is as lighter weight and less costly alternatives to many metallic structures. Nowhere is this promise greater than with respect to building vehicle bodies and components for use on land, sea or in the air.
Factors such as material and labor costs, reduced energy consumption, improved human comfort and safety and increased product durability offer increased incentives for the use of plastic or synthetic materials to replace metal. Today reinforced or composite plastic materials increasingly are being utilized in vehicle bodies and in other structural applications as direct substitutes for metal.
In addition to eliminating corrosion, plastic or resin based composites offer the opportunity of significantly reduced vehicular weight thereby lowering fuel consumption and also providing improved sound and thermal insulation qualities for enhanced passenger comfort. It is the purpose of the present invention to provide composite structures to more effectively achieve these and other objectives.
One of the important concepts of the present unique composite structure is in utilizing plural layers of chemically compatible open-cell foam materials having substantially different compressive resistances whereby during a single low pressure molding operation differing amounts of cured resin are retained in the various foam layers.